Display screen or a portion thereof with a graphical user interface



FIG. 1 is a front view of a display screen or a portion thereof with a graphical user interface.

FIG. 2 is a front view of a second embodiment thereof; and,

FIG. 3 is a front view of a third embodiment thereof.

The dash-dot-dash broken lines shown on the graphical user interface form no part of the claimed design.

In all of the figures, the outermost broken lines forming a dash-dash line pattern show a display screen or a portion thereof, and form no part of the claimed design. 

CLAIM The ornamental design for a display screen or portion thereof with a graphical user interface, as shown and described. 